The city Campaign Finance Board sided with Mayor Bloomberg yesterday in a case against his 2009 campaign that ended with a political operative going to jail.

The board ruled 3-1 against a complaint that said Bloomberg should have disclosed a $1.2 million donation to the state Independence Party to help him with an Election Day poll-watching operation.

The board said Bloomberg — a billionaire independent who personally financed his campaign against Democrat Bill Thompson — did not have to disclose the donation to the state Independence Party, which in turn gave it to GOP operative John Haggerty, who stole $750,000.

Haggerty was eventually convicted and sentenced to serve 1 1/3 to four years in prison for the theft.

The CFB made a similar ruling in 2009, when Thompson complained about Bloomberg’s massive donations over the years to the state Republican Party’s housekeeping account.

At that time, the board ruled that beginning in January 2010, all candidates who donate at least $100 to a political party in New York state would have to formally report it.

Bloomberg’s donation still falls out of that time frame, which is why the board sided with him.

Still, the board admonished the freewheeling process of giving to political parties in the state, and recommended that parties file more frequent disclosure forms.

It also said candidates’ donations should have a cap. The CFB did not recommend an amount.